Though green ash is not the most susceptible ash species to anthracnose infection, occurrence is still a possibility. This fungus disease may cause significant damage to your home landscape, especially if left untreated. Get to know what to look for, and identify control and avoidance methods to prevent injury to your healthy garden.
Healthy trees are less susceptible to infection by fungus than weakened trees or those already in decline. Plant green ash trees in locations that offer full sunlight. Green ashes thrive in moist, wet and dry soil, and tolerate all soil types, from sand to clay. Ideal pH is 3.7 to 8.2, according to the Virginia Cooperative Extension. However, avoid waterlogged soil, which creates an ideal environment for fungi germination.
Ash anthracnose is caused by the fungus Apiognomonia errabunda, affecting white ash most prevalently. Though green ash has shown signs of resistance, it is also susceptible to infection. Anthracnose fungus problems appear in spring during cool, wet weather, according to the University of Rhode Island Landscape Horticulture Program. The fungi overwinter on trees and plant debris and spread sporadically on wind and rain.
Green ash anthracnose fungus results in the formation of lesions that appear water-saturated on shoots and leaves. The spots expand and change in color from green to brown. The growth of the lesion's tissue ceases, and as the rest of the plant grows, the affected areas become deformed, according to the University of Rhode Island's program. Trees may suffer from diminished health and severe leaf drop.
Planting resistant ash trees and avoiding highly susceptible species is an effective preventive measure and is a good solution when replanting after an infection has occurred. For anthracnose fungus avoidance, do not plant the vulnerable F. velutina 'Modesto' tree. However, do select F. Uhdei 'Shamel' or F. oxycarpa 'Raywood,' as these are known for their resistance, according to the University of California IPM Online. Because resistance varies from region to region, contact your local county extension agent for specifics.
For control of anthracnose fungus on green ash, remove and destroy reachable, affected plant parts to prevent localized and widespread transfer of disease. Sanitize pruning tools between each use and from one tree to the next to avoid disease transfer. For chemical control, apply a fungicide containing the active ingredient chlorothalonil or mancozeb at budbreak, according to the University of Minnesota Extension.